S355K2G2W Weathering Steel Impact Energy Requirements Explained

S355K2G2W's "K2" marking guarantees specific impact toughness. Understanding it prevents certificate confusion.

The requirement. At -20°C, three Charpy V-notch specimens from the same plate must average at least 27J. No single value may fall below 20J.

Specimen size matters. The 27J applies to full-size specimens (10 × 10mm). For thinner plates, subsize specimens with proportionally lower requirements are used:

What the certificate should show. Test temperature (-20°C), specimen size, three individual values, average, and standard reference (EN 10025-5 or EN ISO 148-1).

K2 vs. J2. Both test at -20°C, but K2 historically required stricter individual limits. In practice, EN 10025-5 applies the same rules to both.

Why it matters. S355K2G2W goes into bridges, railcars, and cold-climate structures. The K2 rating ensures the steel absorbs impact energy rather than fracturing when winter arrives.

Common pitfall. Checking only the average. Verify individual values too—a single low value below 20J fails the requirement, even if the average meets 27J.

What if impact values are borderline? For critical structures, request supplementary testing on additional specimens or at a lower temperature.